1. Field of the Invention
This invention relates to a tapered roller bearing that is used, for example in the transfer or differential gear mechanism for a manual transmission (M/T) or automatic transmission (A/T) of an automobile, and more particularly to a tapered roller bearing that is capable of suppressing the generation of edge loading when the axis of the outer race crosses the axis of the inner race, and lengthening the life of the bearing.
2. Description of the Related Art
In the case of a roller bearing having a plurality of cilindrical or tapered rolling members (called rollers below), when the axis of the outer race and the axis of the inner race shift such that they cross with each other, a rise in localized contact pressure (edge load) is generated on one side of the contact area between the raceway of the outer race and the rollers or between the raceway of the inner race and the rollers or both, and there is a possibility that this edge loading could cause early damage to the bearing. In addition, when installing the roller bearing into an apparatus, it is necessary to line up the axis of the outer race with the axis of the inner race with high precision. However, when there is a possibility that as the rotating shaft bends due to large axial loads, these axes will shift.
For example, when the tapered roller bearing that is used in the output-shaft side of the transaxial (mechanism which houses the clutch, transmission and reduction gear in the same housing) for the M/T or A/T of an automobile is misaligned (for example, in a state where the axis of the outer race crosses the axis of the inner race) due to excessive loading from the reaction force of the output shaft gear or due to a decrease in rigidity of the housing, edge loading may occur at the end of the raceway surface or end of the roller to shorten the life of the bearing.
In order to avoid this kind of problem, the operating conditions of the bearing were improved instead of improving the tapered roller bearing itself. For example, the allowable inclination angle of the tapered roller bearing was made to be 0.0009 radians (3 minutes), and so the installation tolerance was regulated, so that no excessive loading occurred, or a high-precision housing or/and shaft was used.
On the other hand, methods of treating the tapered roller bearing itself, such as using a tapered roller bearing for which crowning processing, such as full crowning or partial crowning, was performed on each of the raceway surfaces or on each of the rolling contact surfaces of the rollers or on both, was also considered. In this case, the crowning process is a process of forming a very small taper or curve on the generatrix of the raceway surface or rolling contact surface.
However, in the case of a tapered roller bearing on which crowning has been performed, it is necessary to make small the radius of curvature of the crowning in order that edge loading does not occur between the raceway surface and rolling contact surface when there is a large angle of shift between the axes. However, by doing this, when the angle of shift between the axes is small, or when there is no shift between the axes, there was a problem in that the surface pressure in the center of the contact area between each of the raceways and rollers becomes high when compared to when crowning is not performed or when the radius of curvature of crowning is large.
Japanese patent publication No. Toku Kai 2000-74075 discloses a tapered roller bearing that is capable of relieving the surface pressure between the raceway surface and each of the rolling contact surfaces in the case when the angle of shift between the axes of the outer race and inner race is small, and suppressing edge loading from occurring in both the case when the angle of shift between the axes of the outer race and inner race is large and also when it is small. This tapered roller bearing is defined by a generatrix having a radius of curvature such that one of the opposite ends of the raceway surfaces of the inner and outer races and the opposite ends of the rolling contact surfaces of the rollers separates from the other.
However, in the case of this bearing, there was a concern that the surface pressure in the center of the contact area between each of the raceway surfaces and the rolling contact surfaces of the rollers would increase when the angle of shift between the axes of the outer and inner races was large.
Therefore, as a result of zealous investigation by the inventors, it was found that in the case of the tapered roller bearing disclosed in Japanese Patent Publication No. Toku Kai 2000-74075, it was possible to suppress edge loading, as well as suppress an increase of surface pressure in the center of the contact area between the raceway surfaces and rolling contact surfaces due to misalignment, by setting an optimum curvature for the raceway surfaces.
It is the object of this invention to provide a tapered roller bearing that is capable of suppressing edge loading, as well as suppressing an increase of surface pressure in the center of the contact area between the raceway surfaces and rolling contact surfaces of the rollers, even when the angle of shift between the axes of the outer and inner races is large.